There is extensive evidence that the human visual system processes spatial information in parallel on several different spatial scales, a process mediated by mechanisms selectively tuned to different orientation and spatial frequency ranges. Previous research supported by this grant has led to accurate quantitative descriptions of the orientation and spatial frequency tuning of these mechanisms, and it has clarified the role they play in both normal and amblyopic pattern discrimination tasks. However, these mechanisms have generally been treated as though they were independent and non-interacting. This leads naturally to the central question of this proposal: in what ways do spatial mechanisms interact, and how do these interactions aid in the processing of complex patterns? The few previous studies of interaction among spatial mechanism generally fall into three categories. First, there is evidence that a sum of high spatial frequency gratings can mask a low spatial frequency (Henning, et. al., 1975), a phenomenon often though to result from nonlinearities at an early level (probably in the receptors). Second, cosine gratings with very different orientations and directions motion can lock to produce coherent motion in a direction different from either one and from their vectors sum (Adelson and Movshon, 1982). Third, the presence of low spatial frequencies in a stereogram can extend the fusional range or diplopia limit for high frequencies in the same image. Preliminary research funded by this grant has produced a powerful masking technique for probing mechanism interactions in coherent motion and has explored interactions between spatial frequencies in stereopsis. Accordingly, the goals of the proposed research are: (1) to determine whether masking of low by high frequencies results from an early (probably receptor) nonlinearity; (2) to elucidate those spatial mechanism interactions underlying coherent, two-dimensional motion; and (3) to determine how spatial mechanisms interact to extend the range of stereopsis. In addition to using similar stimulus configurations, experiments in al areas will utilize similar masking and discrimination paradigms. This research should greatly expand our understanding of the manner in which mechanism interactions aid in processing complex visual information.